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Biology > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

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1
Q
  1. What elements are nucleic acids made from?
A

Carbon, hydrogen, oxygen, nitrogen and PHOSPHOROUS

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2
Q
  1. What are the building blocks of nucleic acids?
A

PHOSPHOROUS They are formed from nucleotides which consist of a phosphate group, a pentose sugar and a nitrogenous base, combined through condensation reactions (removal of water)

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3
Q
  1. How do nucleotides form polynucleotides and nucleic acids?
A

PHOSPHODIESTER bonds, which form between the phosphate of one nucleotide and the pentose sugar of the next nucleotide, to form long chains of polynucleotides (hydrolysis will reverse this). Nucleic acids are formed from further condensation of these polynucleotide chains

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4
Q

Describe DNA

A

DNA is a double helix, composed of two antiparallel polynucleotide chains joined via hydrogen bonds between their nitrogenous bases. Base pairing occurs between Adenine and Thymine and between Guanine and Cytosine. The nucleotides that make up the polynucleotides contain the sugar deoxyribose.

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5
Q
  1. Name an important nucleotide in our bodies and give its function
A

ATP, Adenosine triphosphate, the molecule that supplies and carries energy in cells.

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6
Q
  1. Name 2 important nucleic acids
A

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

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7
Q
  1. Describe RNA
A

RNA is a single polynucleotide chain made up from nucleotides containing the sugar, ribose. Like DNA, the nucleotides are joined via phosphodiester bonds but the nitrogenous bases are Adenine, Uracil, Guanine and Cytosine

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8
Q
  1. What are the 3 types of RNA?
A
  • Messenger RNA (carries DNA code from nucleus to a ribosome in the cytoplasm * Transfer RNA (carries amino acids to mRna on ribosome) * Ribosomal RNA (forms the ribosome, made in nucleolus)
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9
Q
  1. What is the role of DNA?
A

Carries the genetic code; the bases it is mad up from form triplet codes (codons) which code for the amino acids that form each protein

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10
Q
  1. Describe (briefly) the semi-conservative theory of DNA
A

The DNA double helix unwinds and a new strand is formed when free nucleotides join up with the exposed bases of each of the template strands by base-pairing. The result is 2 new DNA molecules, each of which contains one original (template) strand and one new DNA strand

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11
Q
  1. What happens during base-pairing?
A

The nucleotides containing the base Adenine bond with the nucleotides containing the base Thymine and those containing Guanine join with those containing Cytosine. Hydrogen bonds form between the bases.

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12
Q
  1. What does DNA helicase do?
A

This enzyme causes the DNA double helix to unwind by breaking the hydrogen bonds between the bases

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12
Q
  1. What does DNA polymerase do?
A

This enzyme helps the new complementary DNA strands to form by catalysing the attachment of the nucleotides to each other via phosphodiester bonds.

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13
Q
  1. What did the conservative theory/model propose?
A

In this model, the parental/original DNA does not unwind but is simply copied to form a new double strand.

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14
Q
  1. Name the famous experiment which proved that the method of DNA replication is semi-conservative
A

The Meselson-Stahl Experiment (1958) (“the most beautiful experiment in Biology!

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15
Q
  1. What were the radioactive isotopes that were used in the Meselson-Stah experiment?
A

N15 and N14(N15 was the heavy isotope, N14 the light one)

16
Q
  1. Why were these specific radioactive isotopes used?
A

Because nitrogen is part of DNA’s structure Specifically, it is found in the bases, A, T , G and C

17
Q
  1. Why was bacterial DNA (E.coli) used in this experiment?
A

Bacteria reproduce very quickly and easily, enabling results to be obtained quickly

18
Q

-he experiment involved growing bacteria initially in a medium containing N15. When they were then transferred to a medium containing N’4 and allowed to replicate for one generation, what did centrifugation show the make-up of the DNA now was.

A

The bacterial DNA was now hybrid DNA, made of half N15 and half NI4 (this is GENERATION 1)

19
Q
  1. If the generation 1 hybrids are now cultured again with N14, what ratios are found in the generation 2 bacterial DNA?
A

50% of the DNA is hybrid N14/15DNA and 50% is lighter N14 DNA (this is GENERATION 2))

20
Q
  1. If allowed to replicate again in a medium containing the light N14 what would you expect the outcome to be?
A

A ratio of 3:1 for light to hybrid (3rd Gen)

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